Seasonal dynamics of iron and phosphorus in reservoir sediments in Eucalyptus plantation region

Background Iron (Fe) and phosphorus (P) dynamics in sediments have direct and indirect impacts on water quality. However, the mobility of P and Fe in reservoir sediments in Eucalyptus plantation region remains unclear. This study examined P and Fe pollution in sediments in a Eucalyptus plantation region using the novel planar optode, the ZrO-Chelex DGT, and the DIFS model. Results Direct in situ investigations showed that the levels of labile P and Fe were smaller in the Eucalyptus species-dominated sediments (X2) compared to sediments without Eucalyptus species (X1). The mean concentration of labile P and Fe decreased by 25% and 42% from X1 to X2. The decrement was insignificant (p = 0.20) in the surface sediment concentration for labile P. The significant disparity for DGT-Fe (Fe2+) (p = 0.03) observed in the surface sediments could be attributed to the Eucalyptus species’ elevated organic matter (tannins) concentration at X2, which reacted and consumed labile Fe. For both regions, the maximum concentration of labile P and Fe occurred in November (autumn). The reductive decomposition of Fe/Mn oxides was recognized as the main driver for their high P efflux in July and November. Low concentration of labile P and Fe was observed in December (winter) due to the adsorption of Fe/Mn oxides. The concentration of labile Fe synchronizes uniformly with that of labile P in both sediments indicating the existence of a coupling relationship (r > 0.8, p < 0.01) in both regions. The positive diffusion fluxes in both regions suggested that the sediments release labile P and Fe. The fluxes of labile P and Fe in both regions were substantially higher (p < 0.05) in the summer (anoxic period) than winter (aerobic period), indicating that hypoxia and redox conditions influenced the seasonal efflux of labile P and Fe. From the DIFS model, the replenishment ability of reactive P was higher during the anoxic period (R = 0.7, k1 = 79.4 day− 1, k-1 = 0.2 day− 1) than the aerobic period (R = 0.4, k1 = 14.2 day− 1, k-1 = 0.1 day− 1), suggesting that oxygen inhibited the efflux of P in the sediments. Conclusion Our results indicated that hypoxia, Eucalyptus species (organic matter (tannins)), and redox conditions influenced the seasonal mobility of sediment labile P and Fe. Our findings provided an insight into the mobility of labile P and Fe in Eucalyptus-dominated sediments and, moreover, serves as a reference for developing future studies on Eucalyptus-dominated sediments.

Use of an Oxygen Planar Optode to Assess the Effect of High Velocity Microsprays on Oxygen Penetration in a Human Dental Biofilms In-Vitro

BackgroundDental plaque biofilms are the causative agents of caries, gingivitis and periodontitis. Both mechanical and chemical strategies are used in routine oral hygiene strategies to reduce plaque build-up. If allowed to mature biofilms can create anoxic microenvironments leading to communities which harbor pathogenic Gram-negative anaerobes. When subjected to high velocity fluid jets and sprays biofilms can be fluidized which disrupts the biofilm structure and allows the more efficient delivery of antimicrobial agents.MethodsTo investigate how such jets may disrupt anoxic niches in the biofilm, we used planar optodes to measure the dissolved oxygen (DO) concentration at the base of in-vitro biofilms grown from human dental saliva and plaque. These biofilms were subject to “shooting” treatments with a commercial high velocity microspray (HVM) device.ResultsHVM treatment resulted in removal of much of the biofilm and a concurrent rapid shift from anoxic to oxic conditions at the base of the surrounding biofilm. We also assessed the impact of HVM treatment on the microbial community by tracking 7 target species by qRT-PCR. There was a general reduction in copy numbers of the universal 16S RNA by approximately 95%, and changes of individual species in the target region ranged from approximately 1 to 4 log reductions.ConclusionWe concluded that high velocity microsprays removed a sufficient amount of biofilm to disrupt the anoxic region at the biofilm-surface interface.

Use of an Oxygen Planar Optode to Assess the Effect of High Velocity Microsprays on Oxygen Penetration in a Human Dental Biofilms In-Vitro

Background Dental plaque biofilms are the causative agents of caries, gingivitis and periodontitis. Both mechanical and chemical strategies are used in routine oral hygiene strategies to reduce plaque build-up. If allowed to mature biofilms can create anoxic microenvironments leading to communities which harbor pathogenic Gram-negative anaerobes. When subjected to high velocity fluid jets and sprays biofilms can be fluidized which disrupts the biofilm structure and allows the more efficient delivery of antimicrobial agents. Methods To investigate how such jets may disrupt anoxic niches in the biofilm, we used planar optodes to measure the dissolved oxygen (DO) concentration at the base of in-vitro biofilms grown from human dental saliva and plaque. These biofilms were subject to “shooting” treatments with a commercial high velocity microspray (HVM) device. Results HVM treatment resulted in removal of much of the biofilm and a concurrent rapid shift from anoxic to oxic conditions at the base of the surrounding biofilm. We also assessed the impact of HVM treatment on the microbial community by tracking 7 target species by qRT-PCR. There was a general reduction in copy numbers of the universal 16S RNA by approximately 95%, and changes of individual species in the target region ranged from approximately 1 to 4 log reductions. Conclusion We concluded that high velocity microsprays removed a sufficient amount of biofilm to disrupt the anoxic region at the biofilm-surface interface.

Use of an Oxygen Planar Optode to Assess the Effect of High Velocity Microsprays on Oxygen Penetration in a Human Dental Biofilms In-Vitro

Background Dental plaque biofilms are the causative agents of caries, gingivitis and periodontitis. Both mechanical and chemical strategies are used in routine oral hygiene strategies to reduce plaque build-up. If allowed to mature biofilms can create anoxic microenvironments leading to communities which harbor pathogenic Gram-negative anaerobes. When subjected to high velocity fluid jets and sprays biofilms can be fluidized which disrupts the biofilm structure and allows the more efficient delivery of antimicrobial agents. Methods To investigate how such jets may disrupt anoxic niches in the biofilm, we used planar optodes to measure the dissolved oxygen (DO) concentration at the base of in-vitro biofilms grown from human dental saliva and plaque. These biofilms were subject to “shooting” treatments with a commercial high velocity microspray (HVM) device. Results HVM treatment resulted in removal of much of the biofilm and a concurrent rapid shift from anoxic to oxic conditions at the base of the surrounding biofilm. We also assessed the impact of HVM treatment on the microbial community by tracking 7 target species by qRT-PCR. There was a general reduction in copy numbers of the universal 16S RNA by approximately 95%, and changes of individual species in the target region ranged from approximately 1 to 4 log reductions. Conclusion We concluded that high velocity microsprays removed a sufficient amount of biofilm to disrupt the anoxic region at the biofilm-surface interface.

The effect of unsteady streamflow and stream-groundwater interactions on oxygen consumption in a sandy streambed

Streamflow dynamics are often ignored when studying biogeochemical processes in the hyporheic zone. We explored the interactive effects of unsteady streamflow and groundwater fluxes on the delivery and consumption of oxygen within the hyporheic zone using a recirculating flume packed with natural sandy sediments. The flume was equipped with a programmable streamflow control and drainage system that was used to impose losing and gaining fluxes. Tracer tests were used to measure hyporheic exchange flux and a planar optode was used to measure subsurface oxygen concentration patterns. It was found that the volume of the oxic zone decreased when the losing flux declined, and was drastically decreased when gaining conditions were applied. It was also found that unsteady streamflow led to a slight increase in the average volume of the oxic zone, compared to the average volume of the oxic zone under steady streamflow. However, the average oxygen consumption rates were significantly higher under unsteady streamflow compared to steady streamflow under all groundwater conditions with the exception of the highest losing flux. The present study provides the first insight into the interactions between streamflow unsteadiness and losing/gaining fluxes and improve understanding of their impact on microbial metabolism in the hyporheic zone.

Use of an Oxygen Planar Optode to Assess the Effect of High Velocity Microsprays on Oxygen Penetration in a Human Dental Biofilms In-Vitro

Background Dental plaque biofilms are the causative agents of caries, gingivitis and periodontitis. Both mechanical and chemical strategies are used in routine oral hygiene strategies to reduce plaque build-up. If allowed to mature biofilms can create anoxic microenvironments leading to communities which harbor pathogenic Gram-negative anaerobes. When subjected to high velocity fluid jets and sprays biofilms can be fluidized which disrupts the biofilm structure and allows the more efficient delivery of antimicrobial agents. Methods To investigate how such jets may disrupt anoxic niches in the biofilm, we used planar optodes to measure the dissolved oxygen (DO) concentration at the base of in-vitro biofilms grown from human dental saliva and plaque. These biofilms were subject to “shooting” treatments with a commercial high velocity microspray (HVM) device. Results HVM treatment resulted in removal of much of the biofilm and a concurrent rapid shift from anoxic to oxic conditions at the base of the surrounding biofilm. We also assessed the impact of HVM treatment on the microbial community by tracking 7 target species by qRT-PCR. There was a general reduction in copy numbers of the universal 16S RNA by approximately 95%, and changes of individual species in the target region ranged from approximately 1 to 4 log reductions. Conclusion We concluded that high velocity microsprays removed a sufficient amount of biofilm to disrupt the anoxic region at the biofilm-surface interface.

Elevated micro-topography boosts growth rates in Salicornia procumbens by amplifying a tidally driven oxygen pump: implications for natural recruitment and restoration

Background and Aims The growth rate of pioneer species is known to be a critical component determining recruitment success of marsh seedlings on tidal flats. By accelerating growth, recruits can reach a larger size at an earlier date, which reduces the length of the disturbance-free window required for successful establishment. Therefore, the pursuit of natural mechanisms that accelerate growth rates at a local scale may lead to a better understanding of the circumstances under which new establishment occurs, and may suggest new insights with which to perform restoration. This study explores how and why changes in local sediment elevation modify the growth rate of recruiting salt marsh pioneers. Methods A mesocosm experiment was designed in which the annual salt marsh pioneer Salicornia procumbens was grown over a series of raised, flat and lowered sediment surfaces, under a variety of tidal inundation regimes and in vertically draining or un-draining sediment. Additional physical tests quantified the effects of these treatments on sediment water-logging and oxygen dynamics, including the use of a planar optode experiment. Key Results In this study, the elevation of sediment micro-topography by 2 cm was the overwhelming driver of plant growth rates. Seedlings grew on average 25 % faster on raised surfaces, which represented a significant increase when compared to other groups. Changes in growth aligned well with the amplifying effect of raised sediment beds on a tidally episodic oxygenation process wherein sediment pore spaces were refreshed by oxygen-rich water at the onset of high tide. Conclusions Overall, the present study suggests this tidally driven oxygen pump as an explanation for commonly observed natural patterns in salt marsh recruitment near drainage channels and atop raised sediment mounds and reveals a promising way forward to promote the establishment of pioneers in the field.